A field-effect transistor (FET) includes a threshold voltage. The threshold voltage is a minimum gate-to-source voltage differential that can create a conducting path between source and drain terminals.
A gate (or gate structure) is provided in the FET. The gate controls the conducting path by applying voltages across a channel. When the voltages apply to the gate, electrical currents flow through the channel. When the voltages stop applying to the gate, electrical currents stop flowing through the channel. The voltage that turn on the FET is the threshold voltage. FETs with different threshold voltages can be combined to generate a reference voltage for different application.